Method of Filtering Liquid Media

ABSTRACT

A method of filtering liquid media comprises directing liquid to be filtered into a vessel under pressure and draining filtered liquid media from the filtration vessel. In backwash mode liquid is forced through filter media effecting rotating flow and fluidisation of the filter media, and in normal operation liquid present in the vessel above the filter media is caused to undergo rotating flow about the vessel. The drain arrangement includes a plurality of radially extending limbs configured to act as backwash liquid distribution means in backwash mode or filtered liquid collection means in normal filter mode. In backwash mode, liquid is distributed in a direction transverse to the longitudinal direction of the respective limbs; and/or the majority of the limbs direct water either clockwise or anticlockwise.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/492,823, filed on Sep. 27, 2004, which is a 371 of PCT/GB02/04705,filed on Oct. 15, 2002, which claims priority from GB 0125141.2, filedOct. 18, 2001, all of which are hereby incorporated herein by referencein their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to filtration of liquid media andparticularly to filtration of water or the like.

2. State of the Art

Filtration apparatus is known for filtering water. Such apparatustypically comprises a vessel pressurised with water having an inlet, abed of filter media (typically one or more layers of graded sand orother particulate material), and an outlet drain arrangement fordirecting off the filtered water. In order to periodically clean thefilter media a cleaning backwash is forced through the drain arrangement(typically causing fluidisation of the bed of filter media) and thebackwashed liquid is drawn off to waste above the level of the bed offilter media.

An improved technique and system has now been devised.

SUMMARY OF THE INVENTION

According to a first aspect, the invention provides filtration apparatusincluding:

-   -   a filtration vessel;    -   an inlet arrangement for inflow into the filtration vessel of        liquid media to be filtered;    -   a body of filter media in the filtration vessel; and    -   a drain arrangement to receive filtered liquid media for take        off from the filtration vessel; wherein:        -   the inlet arrangement is configured to induce substantially            rotating flow about the vessel of unfiltered liquid present            in the vessel; and/or,        -   the drain arrangement is configured in backwash mode to            force backwash liquid through the filter media in            substantially rotating flow about the vessel; and/or        -   the drain arrangement includes a plurality of drain limbs            inclined to the horizontal and providing for draining of            filtered liquid along the inclined limbs to outlet the            apparatus.

It is preferred that the inlet arrangement comprises liquid directingmeans arranged to direct pressurised liquid along a tangential orcircumferential path with respect to an axis of the vessel.Beneficially, the liquid directing means is arranged to direct thepressurised liquid entering the vessel at an acute angle downwardly.

Beneficially, the inlet arrangement is provided closely adjacent theupper internal surface of the vessel, which upper internal surface ofthe vessel is beneficially inclined or concave from an upper point tolower portions proximate the periphery of the vessel. This aids inpromoting the rotating flow.

Typically the unfiltered water is pressurised in the vessel above thelevel of the filtration media (which is typically present as a bedlaying in the vessel). The inlet arrangement is designed to induce aflow pattern within the vessel to maximise the flow length from theinlet arrangement to the liquid/filter media interface. Creating arotation from stimulus at the inlet arrangement zone in the liquid spaceabove the filter media provides a body or bulk rotation of the liquidmedia about the axis of the vessel and ensures:

-   1. Even flow of liquid media through the filter media bed;-   2. Minimal eddy currents at higher flow rates to ensure pressure    balance at water/filter media interface and inhibit tunnelling    through the filter media; and-   3. Retention of flocs on the surface of the filter media at high    rates of flow.

In Northern Hemisphere environments the rotation is to be induced in aclockwise direction, whereas in Southern Hemisphere locationsanticlockwise rotation is necessary. The reason for the differentdirection of rotation preferred is due to the coriolis force caused bythe earth's rotation. Taking advantage of the coriolis force leads topreferred rotation in different directions in Northern and SouthernHemispheres.

The inlet arrangement preferably comprises a plurality of radiallyextending duct arms, each including outlet means (typically apertures)to direct pressurised unfiltered liquid transversely to the radialdirection. The duct arms are configured to direct the outlet liquideither substantially in a clockwise sense or in an anticlockwise sense(dependant upon the geographical location of the filter vessel either inthe Northern or Southern Hemisphere).

Beneficially, the radial duct arms are regularly spaced about an axis,preferably connected to a central or hub plenum inlet chamber.Beneficially the radial duct arm outlet apertures, direct thepressurised liquid at an acute angle outwardly and downwardly from theinlet arrangement within the vessel.

Beneficially the outlet apertures are guarded by filter or mesh means toinhibit filter media or other detritus passing back through the inletarrangement during the backwash cycle.

It is preferred that the drain arrangement includes a plurality ofradially extending limbs, each preferably including apertures, slots orother liquid passage means to act as backwash liquid distribution meansin backwash mode or filtered liquid collection means in normal ‘filtermode’. The backwash liquid distribution means (apertures etc) isbeneficially configured to distribute backwash liquid in a directiontransverse to the longitudinal direction of the respective limbs.Beneficially the backwash outlet means of limbs in the drain arrangementis configured such that in backwash mode the majority (or all) of thelimbs direct water in either a clockwise sense or alternatively ananticlockwise sense (depending again upon the geographical location ofthe filter vessel in either the Northern or Southern Hemisphere).

The backwash outlet means of the radial limbs of the drain arrangementalso serve to collect the filtered liquid (in filter mode) having passedthrough the body of filter media.

The drain arrangement is preferably positioned toward the interior baseof the vessel. Beneficially the interior base of the vessel is inclined,concave or dish shaped, the radial limbs of the drain arrangementextending from a lower most end at a radial central zone of the vesselto an upper end raised from the lower end and radially spaced from thecentre of the vessel. The radial limbs are therefore effectivelyinclined, and preferably connect with a radially central drain chamber.Because the limbs are inclined, draining of the filtered liquid into thedrain chamber is improved. The limbs can extend at the lowest possiblepoint in the vessel with respect to the inclined, concave or dish shapedinterior bottom surface of the vessel. Prior art arrangements have hadnon-radially configured limbs of a drain arrangement extendingsubstantially horizontally.

Beneficially the apertures providing the backwash outlet or filter mediainlet to the drain arrangement are provided over the majority of thelength of the radial limb. Slots or the like may be provided at spacedintervals along the length of the limb to achieve this. Beneficially theapertures are provided with filter or mesh guard means to inhibit filtermedia entering the drain arrangement.

In backwash mode high flow rates are used to ensure efficient backwashcycle without loss of filter media. The purpose of the backwash cycle isto attempt to remove detritus from the body of filter media, includinginhibiting the risk of growth of pathogen colonies within the media.This reduces deterioration of the filter performance. This in turn aidsin extending the life of the filter media. High flow rates are preferredin the backwash cycle in order to provide a short and efficient backwashcycle reducing the water volume used and further minimising runningcosts.

According to a further aspect, the invention provides a method offiltering liquid media, the method comprising directing liquid to befiltered into a vessel under pressure, the vessel including a bed offilter media and a drain arrangement for take-off of filtered liquidmedia from the filtration vessel, wherein liquid present in the vesselabove the bed of filter media is caused to undergo rotating flow aboutthe vessel and/or wherein in backwash mode liquid is forced through thefilter media effecting rotating flow and fluidisation of the filtermedia.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described in specific embodiments byway of example only with reference to the accompanying drawings inwhich:

FIG. 1 is a schematic view of a first embodiment of filtration apparatusaccording to the invention;

FIG. 2 is a plan view of drain arrangement of the filter apparatus ofFIG. 1;

FIGS. 3 a, 3 b, and 3 c are plan, side and detail views of a liquidinlet arrangement in accordance with the apparatus of the invention;

FIGS. 4 a, 4 b, and 4 c are section, side and detail views of analternative embodiment of liquid inlet arrangement; and

FIG. 5 is a schematic side view of a limb of the drain arrangement suchas the drain arrangement shown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, and initially to FIG. 1, there is shown apressure sand filter 1 comprising a filter vessel 2 having a liquidinlet arrangement 3 and a filtered liquid drain arrangement 4. Drainarrangement 4 also operates to supply backwash liquid in ‘backwash mode’(as will be described hereinafter).

The vessel 2 has a concave internal bottom 5 upon which rests a bed offilter media 6 extending upwardly to approximately half the depth of thevessel 2. Filter media typically comprises a body of particulatematerials such as filter sand which may be single-grade or multi-gradedepending upon the precise application of the filter. Activatedcharcoal/carbon or other particulate material may also be utilised.Liquid (water) to be filtered is directed under pressure into the vessel2 via inlet arrangement 3 such that the pressurised head volume 8 ofliquid is present above the surface 7 of filter media bed 6 in headspace 8.

An important aspect of the invention is the ability of the inletarrangement 3 to direct pressurised unfiltered inlet liquid such thatupon entry into the head space 8 bulk rotation of liquid in head space 8is created about the central axis of the vessel 2. Such an effectenables a situation approaching hydraulic balance to be achieved at theliquid/filter media interface providing even flow through the filterbed, minimising eddy currents and avoiding tunnelling into the filtermedia.

In order to achieve this the liquid inlet comprises a filter head 10having a plurality of regularly spaced radial arms 11 extendingoutwardly from a central plenum 12. Central plenum 12 includesperforations permitting unfiltered liquid media to enter directly intohead space 8, although a large proportion of the liquid entering isdirected via arms 11 as will be described hereafter.

Arms 11 communicate with plenum 12 and are generally tubular incross-section (as shown most clearly in FIG. 3 c). Respective angledslots 13 are provided for each of limbs 11, slots 13 being configured todirect jetting pressurised liquid out of arm 11 in a directiontransverse to the longitudinal direction to arm 11. As can be seen fromFIG. 3 c, the slots 13 are arranged to direct the outlet jetting liquidalso at an inclined angle downwardly into the vessel.

FIG. 3 c shows an alternative slot 13 a. It should be noted that slots13 and 13 a are not provided in a single embodiment. Slots 13 and 13 aare provided as alternatives for use in Northern and SouthernHemispheres where contra-sense rotation of the liquid in head space 8 isrequired.

Referring to FIG. 3 a, each limb 11 directs liquid tangentially(transversely to the longitudinal direction of respective arms 11) inthe direction of arrows X. This directional jetting of inlet liquid issufficient to initiate the required rotating flow in the body ofpressurised liquid in head space 8.

Referring to FIG. 4 and 4 a, an alternative arrangement 103 is disclosedcomprising a central plenum hub 112, and a series of curve-form vanes111 regularly angularly spaced about hub 112 and extending outward awayfrom the central plenum hub 112. The lower surface 120 of the inletarrangement 103 includes a series of radially extending angularly spacedslots 113 and a welded deflection plate 115 to direct the pressurisedliquid in the required inlet direction into the interior of vessel 2.Vanes 111 direct the water entering into the inlet arrangement radiallyoutwardly some being forced through slots 113 and some exitingtangentially between outlet apertures formed between the distal ends ofvanes 111 and the back of an adjacent vane.

The drain arrangement 4 (shown most clearly in FIGS. 1, 2 and 5)comprises a series of angularly spaced radially extending limbs 20communicating with an axial drain chamber 21. The limbs effectively restas closely as possible upon the concave base 5 of vessel 2, extending ininclined fashion upwardly from drain chamber 21 to their respectivedistal radially outermost ends. This is a departure from typical priorart arrangements in which a network of perpendicularly crossing lateraldrain limbs are provided, mounted on a concrete or other solid base inhorizontal fashion. The inclined orientation of the drain limbs 20provides for draining into a central drain chamber or hub is believed tobe novel and inventive per se.

Referring now to FIG. 5 and FIG. 2 in particular, each radial limb 20comprises aperture means permitting filtered liquid to enter (andbackwash liquid to leave) via a preferred side of the relevant limb. Thepreferred side is common to the majority or all of the limbs 20 in theradial arrangement. In the embodiment shown, a series of substantialregularly spaced slots 25 are provided substantially along the entirelength of the relevant side of the respective limb 20. Slots 25 arecovered with a fine stainless steel mesh 26 to ensure that sand filtermedia does not enter into the drain arrangement 4. In backwash mode,backwash water pumped back through drain arrangement 4 is forced throughthe apertures 25 which, being directed in a common rotational sense forall limbs 20 in drain arrangement 4, results in fluidisation of thefilter media bed 6 and bulk rotation in a common sense of the body offilter material about the central axis of vessel 2. Fluidisation androtation of the filter bed has been found to improve the backwasheffectiveness.

By mounting the drain limbs directly in sand filter media (rather thantypical prior art mounting in gravel on a concrete base) the backwashfluidisation and rotation of the sand filter bed is achieved. Thisarrangement is believed to be novel and inventive per se.

The present invention provides improvements in relation to performanceof filter apparatus by improving the inlet distribution of liquid to befiltered into a filter vessel and also the drain outlet and backwashcapability and efficiency.

There have been described and illustrated herein several embodiments ofa filtration apparatus and corresponding method of operation. Whileparticular embodiments of the invention have been described, it is notintended that the invention be limited thereto, as it is intended thatthe invention be as broad in scope as the art will allow and that thespecification be read likewise. It will therefore be appreciated bythose skilled in the art that yet other modifications could be made tothe provided invention without deviating from its spirit and scope asclaimed.

1. A method of filtering liquid media, the method comprising: directingliquid to be filtered into a vessel under pressure, the vessel includinga bed of filter media and a drain arrangement for take-off of filteredliquid media from the filtration vessel, wherein in backwash mode liquidis forced through the filter media effecting rotating flow andfluidisation of the filter media and wherein in normal operation liquidpresent in the vessel above the bed of filter media is caused to undergorotating flow about the vessel.
 2. A method according to claim 1,wherein: in backwash mode backwash liquid is pumped through the drainarrangement into the vessel.
 3. A method according to claim 2, wherein:the drain arrangement includes a plurality of radially extending limbs.4. A method according to claim 3, wherein: the limbs of the drainarrangement include apertures, slots or other liquid passage means toact as backwash liquid distribution means in backwash mode or filteredliquid collection means in normal ‘filter mode’.
 5. A method accordingto claim 1, wherein: the drain arrangement includes a plurality ofradially extending limbs, backwash liquid distribution means beingconfigured to distribute backwash liquid in a direction transverse tothe longitudinal direction of the respective limbs.
 6. A methodaccording to claim 1, wherein: the drain arrangement includes aplurality of radially extending limbs, backwash outlet means of limbs inthe drain arrangement being configured such that in backwash mode themajority of the limbs direct water in either a clockwise sense oralternatively an anticlockwise sense.
 7. A method according to claim 1,wherein: the drain arrangement is mounted directly in sand filter media.8. A method according to claim 1, wherein: in backwash mode bulkrotation of the filter bed occurs.